1. Field of the Invention
The invention relates to a time-locking method for a local loop network comprising a plurality of stations which are distributed along a bus, each station being connected to the bus by way of a coupler, said bus comprising a looping unit inserted in the bus, said method comprising inter alia an initialization phase for allocating to each station a time reference with respect to a master clock of the looping unit.
2. Description of the Prior Art
A method of this kind is used in a local loop network which is described in U.S. Pat. Ser. No. 235,291, filed Feb. 17, 1981, now U.S. Pat. No. 4,430,699. Information transmitted by an arbitrary station forming part of the local loop network circulates on the bus from coupler to coupler. The looping unit provides the main synchronization of the network and each of the stations synchronizes itself during the initialization phase, for example, with the aid of a phase-locked loop which enables the station to find this synchronization. The looping unit acts as the "master" and the couplers act as "slaves". The transmission of the information between the coupler and the station itself requires a given period of time because the information must travel through the link which connects the station to the coupler. The following problem occurs: a station which is coupled to the bus has access to data circulating on the bus only during a period t.sub.1 after their passage at the level of the coupler. Information transmitted by the station requires a period t.sub.2 in order to travel from the station to the coupler (t.sub.2 represents the propagation time in the link between the station and the coupler). This means that during the period t.sub.1 +t.sub.2 the bus will be unoccupied, so that the bus is used less efficiently.